1. Field of the Invention
The present invention relates to a recording material which is useful when used for thermal transfer printing, especially for melting type thermal transfer printing.
2. Description of the Relates Art
Examples of the conventional recording methods include melting type thermal transfer, sublimation type thermal transfer, electrophotography, inkjet printing and the like. Among these methods, the melting type thermal transfer method is especially getting attention because the method may allow significantly small size of a device due to its small consumption of energy and also has excellent storage property due to its use of pigment ink.
The qualities which a recording material (image receiving paper) for the melting type thermal transfer is required to possess are as follows:
(1) The dot reproduction of highlighted portions is satisfactory.
(2) The clearness and the concentration of developed colors of image are excellent.
(3) The tone reproduction is satisfactory and image is smooth.
(4) The recording material and image thereon are water proof and no change is caused even if the image or the material catches moisture.
(5) The recording material and image thereon are light resistant and no fading of colors occurs in the image even if the image is left indoor or outdoor in a bright condition.
Various techniques for improvement have been developed in order to satisfy the qualities described above.
In recent years, as the use of digital steel cameras, digital video cameras and the like is increasing common, there has been generated a strong demand for instantly obtaining images of as high quality as silver salt photos. Therefore, the image quality of a printer is now intensely being improved so as to have higher precision.
For example, Japanese Patent Application Laid-Open No. 8-90944 proposes a recording material (image receiving paper) which is excellent in high precision dot reproduction and is applicable to the melting type thermal transfer, as well. In the recording material according to this proposal, the ink receiving layer formed in the substrate surface is provided as a macromolecular porous layer, the density and pore diameter of pores of the porous layer is specified and the pores are formed continuous with each other rather than independent from each other, so that the high precision reproduction is excellently achieved.
However, in recent years, printers are being improved so as to have a more compact size and be energy efficient in consideration of good portability thereof. As a result, recent printers are facing a problem of a smaller amount of heat generated at the head and a smaller printing pressure, which could cause poor ink fixing and dot reproduction. As the recording material of the invention according to aforementioned proposal has not been developed in consideration of the use in such a printer of recent type, the recording material cannot achieve satisfactory image quality when used in a printer of the recent type.
In the case of the conventional, common recording materials including the recording material of the invention according to the aforementioned proposal, even if the surface of the recording material is somewhat rough, highly precise printing is still possible as long as the amount of heat generated at the head is relatively large and the printing pressure is relatively high. However, when the amount of heat generated at the head is relatively small and the printing pressure is relatively low, there arises a problem that the dot reproduction is poor and the transfer property of dots of highlighted portions, in particular, is badly affected.
Accordingly, in consideration of the aforementioned problems associated with the conventional recording material used for the melting type thermal transfer method, the present invention has an object of providing a recording material which can cope with highly precise image even if the amount of heat generated at the head is small and the printing pressure is low, i.e., a recording material having excellent dot reproduction and excellent dot transfer of highlighted portions.
In order to achieve the object, in a first aspect of the present invention, a recording material in which an ink receiving layer containing at least a resin and a pigment is provided on a substrate is characterized in that the ink receiving layer is porous, apparent density thereof is 0.2 to 0.8 g/cm3 and heat conductivity of the ink receiving layer and the substrate is 0.1 to 0.25 W/mxc2x7K.
In a second aspect of the present invention, the recording material in which an ink receiving layer containing at least a resin and a pigment is provided on a substrate is characterized in that the ink receiving layer is porous, apparent density thereof is 0.2 to 0.8 g/cm3 and center line average roughness of the ink receiving layer surface is 0.20 to 0.45 xcexcm.
In the recording material of the first aspect of the present invention, the center line average roughness of the ink receiving layer surface may be set within the range of 0.20 to 0.45 xcexcm. Further, in the recording material of the first or the second aspect, the recording material may have a structure in which the average pore diameter of the ink receiving layer surface is 0.05 to 1 xcexcm, or a structure in which statical coefficient of friction observed between the ink receiving layer surface and the recording material back surface is 0.1 to 0.7, dynamical coefficient of friction observed between the same two surfaces is 0.1 to 0.6 and the stiffness of the recording material in the longitudinal direction thereof is 40 to 300 cm3 when measured according to JIS P 8143. Yet further, the ink receiving layer of the recording material of the first or the second aspect of the present invention may be formed by the steps of: dissolving the resin in a solvent and coating the dissolved resin on the substrate; then immersing the substrate in a liquid to which the solvent is soluble but the resin is insoluble, to allow the resin coating to solidify; and drying the product.
In short, the recording material of the present invention includes a substrate and a porous ink receiving layer formed at least one surface of the substrate. By maintaining the apparent density of the ink receiving layer at an adequate level and decreasing the heat conductivity or decreasing the center line average roughness of the ink receiving layer surface, and further by setting the average pore diameter of the ink receiving layer surface at an appropriate size, the dot reproduction property and the dot transfer property of highlighted portions are significantly improved.